Teaching the student Japanese is the school's duty. Most school districts these days have a Japanese tutor who pops in at least once a week to work with foreign born students. Too bad yours does not. But the regular teachers must be covering that. Kyoto-sensei or someone with a free period works with the student one on one fairly regularly, right?
The school staff or the student's guardian should be the one making phone calls. If you come across something useful in that 5 second Google search, share it with the homeroom teacher, but it's not your business to get involved with the students` private lives. I'm an ALT myself, and it's my feeling that we can do better work when we work around the edges, from the outside looking in, so to speak.
It sounds like you feel that you are being dumped on. Are you direct hire of dispatch? I only ask as it might make a difference in how you want to approach it.